Any material, whether natural or synthetic must exhibit satisfactory resistance to degradation under conditions of use, if products made from the materials are to find a lasting market. A lack of satisfactory resistance to degradation usually manifests itself as a partial or total loss of structure integrity, a darkening or discoloration of the product, a loss of flexibility or resilience, or a combination of the above phenomena. These phenomena are promoted or catalyzed by air (oxygen), heat and light, and are particularly susceptible to autooxidation at elevated temperatures in the presence of oxygen.
To protect organic materials, ingredients which can be collectively called stabilizers are admixed with the materials to prevent or inhibit degradation. These stabilizers work in diverse and complex ways, such that a compound which stabilizes against oxygen degradation in one type of material may be relatively inactive in another type of material. Thus compounds which are stabilizers are further classed as anti-oxidants, antiozonants, heat stabilizers and ultraviolet (UV) light stabilizers, depending upon what type of activity and stabilization they best demonstrate. In many cases, to obtain optimum protection, a mixture of compounds, each specifically selected to afford maximum protection against a certain type of degradation, is often used. In some instances stabilizers are deliberately chosen to counter the adverse effects of a plasticizer which, though highly effective as a plasticizer, tends to accelerate oxygen and heat degradation. In other words, the plasticized material is more susceptible to degradation than if no plasticizer was added. As a general empirical rule, it is found that plasticizers are marginally effective as stabilizers, and stabilizers are marginally effective as plasticizers, it being more likely that a compound with desirable stabilizer properties has undesirable plasticizer properties, and vice versa.
The stabilization of rubber, and particularly synthetic "natural rubber", is essential for its proper functioning and long life. To protect rubber against deterioration, many new compounds have been synthesized and tested. Although most anti-oxidants give good protection as stabilizers, not all stabilizers give satisfactory anti-oxidant activity (Encyclopedia of Polymer Science and Technology, Vol. 12, btm p 267, Interscience Publishers, New York, 1970). The compounds of this invention are primarily antioxidants though they exhibit other desirable stabilizing properties, and are particularly for use in synthetic ester lubricants, generally known as "functional fluids", and in synthetic diene rubbers, as a primary antioxidant, i.e. as the sole antioxidant, or if desired, may be combined with a secondary antioxidant which serves to enhance the stabilizing performance of the primary antioxidant. When used with a secondary antioxidant, the stabilizing effect achieved is synergistic and the performance substantially exceeds the sum total of the performances exhibited by the individual antioxidant components.
The time-tested rubber antioxidants chemically classed as amines and phenols and their respective derivatives are still being used, but newer antioxidants combine a hindered phenol group with another group containing sulfides, triazine, phosphates, phosphites, etc. with the hope that the active materials will combine the advantages of two or more stabilizing moieties.
The compounds of this invention do not belong to any well-recognized chemical class of antioxidants. They are substituted acetamides, and more particularly substituted .alpha.-aminoacetamides. It is worth noting that known antioxidants formed by reactions of aldehyde-amines have only fair oxygen aging, and reaction products of ketone-amines generally have only good oxygen aging (Kirk & Othmer, Encyclopedia of Chemical Technology, 2d Edition, Vol 17, p 526, Interscience Publishers, New York, 1968).
As is well-known to those skilled in the art, the effectivness of an antioxidant organic is predicated upon the oxidizable material in which the antioxidant is used. Thus, though antioxidants are used in plastics, elastomers, petroleum products, synthetic lubricants, food products, paints, soaps and cosmetics, it is seldom that the same type of antioxidant will be useful in a plastic or elastomer, and a petroleum or synthetic lubricant. Yet the compounds of this invention provide just such a multifunctional purpose, being useful in several synthetic resinous materials including plastics, elastomers and particularly conjugated diene polymers and synthetic functional fluids of the type generally classed as di- and polycarboxylate type ester lubricants.
Various amides have been found useful as antioxidants. For example, water-soluble antioxidants such as amides of phenol substituted acids have been produced by reaction of reactive derivatives of corresponding acids with corresponding amino compounds to form acid amides, as disclosed in U.S. Pat. No. 3,665,031. Conventional methods of amide preparation also yield alkylhydroxybenzylamides as taught in U.S. Pat. No. 3,780,103. A reaction between selected alkylaminophenols and thiodialkanoyl acid chlorides yields thiodialkanoamidophenol compounds; related compounds are disclosed in U.S. Pat. Nos. 3,676,494; 3,679,744 and 3,694,375. None of the foregoing conventional methods of amide preparation yields the compounds of this invention.
It was known a long time ago, that the reaction of chloretone (1,1,1-trichloro-2-methyl-2-propanol) with aniline and KOH in ethanol, yields .alpha.-phenylaminoisobutyric acid anilide, also referred to as .alpha.-dimethyl,.alpha.-analino,analinoacetamide (see Example 8B herein), though in poor yields. See G. Banti, Gazz. Chim. Ital. 59, 819-24 (1929). Furthermore, this reaction is applicable only to aniline and substituted anilines, and even so, compounds higher in molecular weight than chloretone and aniline, give progressively poorer yields.
The present invention is particularly directed to (a) novel antioxidants and heat stabilizers classed as hindered acetamides, more specifically classed as hindered alpha-aminoacetamides, (b) novel compositions in which the .alpha.-aminoacetamides are incorporated, and (c) novel syntheses for the .alpha.-aminoacetamides. The basic structure of these novel compounds is an .alpha.-aminoacetamide which is preferably polysubstituted. Though these novel compounds are acyclic, they may have cyclizable substituents, and may form dimers and bis-compounds. The novel compounds of this invention are unrelated to amino acids and are not derived from them.
The synthesis of the novel stabilizers of this invention is made possible by the peculiar action of certain onium salts in an aqueous alkaline medium, which action facilitates the interaction of an amine nucleophilic agent such as a primary or secondary amine, with chloroform or other dichlorocarbene generating agent, and a ketone, aldehyde, cyanohydrin or other alkoxide ion generating agent. The organic onium salts of nitrogen, phosphorus and sulfur are well known. They are ionized in aqueous solutions to form stable cations. Certain onium salts have provided the basis for phase transfer catalysis in a wide variety of reactions, a recent and comprehensive review of which is contained in Angewandte Chemie, International Edition in English, 16 493-558 (August 1977). Discussed therein are various anion transfer reactions where the onium salt exchanges its original anion for other anions in the aqueous phase. These ion pairs can then enter a water immiscible, organic liquid phase, making it possible to carry out chemistry there with the transported anion, including OH.sup.- ions. Many reactions involving water immiscible solutions of various simple organic molecules have been described. However, there is nothing to suggest the phase transfer catalysis of the reactants described in my invention.